Radio telescopes reveal unseen galactic cannibalism

Jun 23, 2008

[B]Mystery of black hole 'feeding' resolved[/B]
Radio-telescope images have revealed previously-unseen galactic cannibalism -- a triggering event that leads to feeding frenzies by gigantic black holes at the cores of galaxies. Astronomers have long suspected that the extra-bright cores of spiral galaxies called Seyfert galaxies are powered by supermassive black holes consuming material. However, they could not see how the material is started on its journey toward the black hole.

One leading theory said that Seyfert galaxies have been disturbed by close encounters with
neighboring galaxies, thus stirring up their gas and bringing more of it within the gravitational
reach of the black hole. However, when astronomers looked at Seyferts with visible-light telescopes, only a small fraction showed any evidence of such an encounter. Now, new images of hydrogen gas in Seyferts made using the National Science Foundation's Very Large Array (VLA) radio telescope show the majority of them are, in fact, disturbed by ongoing encounters with neighbor galaxies.

"The VLA lifted the veil on what's really happening with these galaxies," said Cheng-Yu Kuo, a graduate student at the University of Virginia. "Looking at the gas in these galaxies clearly showed that they are snacking on their neighbors. This is a dramatic contrast with their
appearance in visible starlight," he added.

The effect of the galactic encounters is to send gas and dust toward the black hole and produce
energy as the material ultimately is consumed. Black holes, concentrations of matter so dense that not even light can escape their gravitational pull, reside at the cores of many galaxies. Depending on how rapidly the black hole is eating, the galaxy can show a wide range of energetic activity. Seyfert galaxies have the mildest version of this activity, while quasars and blazars are hundreds of times more powerful.

The astronomers picked a number of relatively nearby Seyfert galaxies that had previously been observed with visible-light telescopes. They then carefully studied the Seyferts with the VLA, specifically looking for radio waves emitted by hydrogen atoms. The VLA images showed the vast majority of the Seyferts were disturbed by encounters with neighbor galaxies.

By comparison, similar VLA images of inactive galaxies showed that very few were disturbed. "This comparison clearly shows a connection between close galactic encounters and the black-hole-powered activity in the cores," said Ya-Wen Tang, who began this work at the Institute of Astronomy & Astrophysics, Academia Sinica (ASIAA), in Taiwan and now is a graduate student at the National Taiwan University.

"This is the best evidence yet for the fueling of Seyfert galaxies. Other mechanisms have been
proposed, but they have shown little if any difference between Seyferts and inactive galaxies," Tang added.

"Our results show that images of the hydrogen gas are a powerful tool for revealing
otherwise-invisible gravitational interactions among galaxies," said Jeremy Lim, also of ASIAA. "This is a welcome advance in our understanding of these objects, made possible by the best and most extensive survey ever made of hydrogen in Seyferts," Lim said.

Source: National Radio Astronomy Observatory

Explore further: Scientists 'map' water vapor in Martian atmosphere

add to favorites email to friend print save as pdf

Related Stories

Hubble sees a galaxy with a glowing heart

Jul 14, 2014

(Phys.org) —This view, captured by the NASA/ESA Hubble Space Telescope, shows a nearby spiral galaxy known as NGC 1433. At about 32 million light-years from Earth, it is a type of very active galaxy known ...

Image: Grand swirls from Hubble

Jun 12, 2014

(Phys.org) —This new Hubble image shows NGC 1566, a beautiful galaxy located approximately 40 million light-years away in the constellation of Dorado (The Dolphinfish). NGC 1566 is an intermediate spiral ...

Image: Hubble peers at the heart of NGC 5793

Mar 24, 2014

(Phys.org) —This new Hubble image is centered on NGC 5793, a spiral galaxy over 150 million light-years away in the constellation of Libra. This galaxy has two particularly striking features: a beautiful ...

Dating our galaxy's dormant volcano

Sep 23, 2013

(Phys.org) —A dormant volcano—a supermassive black hole—lies at the heart of our galaxy. Fresh evidence suggests that it last erupted two million years ago.

Recommended for you

Scientists 'map' water vapor in Martian atmosphere

30 minutes ago

Russian scientists from the Space Research Institute of the Russian Academy of Sciences and the Moscow Institute of Physics and Technology (MIPT), together with their French and American colleagues, have ...

Water fleas prepared for trip to space

5 hours ago

Local 'Daphnia' waterfleas are currently being prepared by scientists at the University of Birmingham for their trip to the International Space Station (ISS), where they will be observed by astronauts.

The worst trip around the world

5 hours ago

As you celebrate the end of the year in the warmth of your home, spare a thought for the organisms riding with a third-class ticket on the International Space Station – bolted to the outside with no protection ...

Four Galileo satellites at ESA test centre

6 hours ago

ESA engineers unwrapped a welcome Christmas present: the latest Galileo satellite. The navigation satellite will undergo a full checkout in Europe's largest satellite test facility to prove its readiness ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

zevkirsh
1 / 5 (2) Jun 23, 2008
giant blackholes exist in the intergalactic space between major galaxies, they cannot be seen , nor detected.
brant
not rated yet Jun 23, 2008
blackholes dont exist.
They are "white" holes. Notice how stuff goes out>>>

The neighboring "snack" is in reality a Birkeland current connecting the 2 galaxies...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.